This invention relates to a method and apparatus for infusing fluids accurately in terms of dosages or infusion rates. In particular it relates to a programmable infusion pump that receives a multiple fluid cartridge.
Infusion pumps are used to administer a variety of drug therapies to patients. Examples of two such diverse applications are the administration of chemotherapy drugs to cancer patients and the administration of heart-rate control drugs to cardiac patients.
The patient receiving drugs which are used to control his heart rate needs to have the fluid delivered at an extremely constant rate because the rate of his heartbeat is proportional (or inversely proportional, as the case may be) to the amount of drug delivered. If the rate of infusion were to decrease or increase significantly, the heart would pump more slowly or more quickly than desired. It is important for the infusion pump administering these drugs to return as quickly as possible to the proper infusion rate.
The volume of a heart rate control drug which was overinfused or underinfused does not have to be corrected for. If, for example, a volumetric correction was made to infuse an additional bolus of drug because the pump had slowed down, the patient might find his heart beating overly fast for a period of time. This would be highly undesirable and might even be dangerous for the patient. This type of therapy is referred to herein as a rate-dependent therapy, and many other examples of such therapies exist.
Another type of therapy which requires an infusion pump is the administration of chemotherapy drugs to cancer patients. A recent trend in the administration of chemotherapy is to provide for a slow, continuous infusion in place of the tradition bolus injection of a cytotoxin. It has been found by many cancer researchers and oncologists that the severe side-effects of chemotherapy, such as nausea, vomiting, diarrhea, anorexia, and lassitude, may be reduced in a significant number of patients if the drugs are administered in lower dosages over a prolonged period of time.
As an example relating to infusion pumps, the dosage of certain cytotoxins which may be administered is determined by approximating the surface area of the skin of the patient. The number of milligrams of drug to be administered for each square meter of skin per day for a given therapy is then computed. This amount of drug may then be administered by the traditional bolus injection in a few seconds or by the more advantageous continuous infusion method over a period of hours or even days.
When the more advantageous continuous infusion method is used, it becomes apparent that the infusion device must endeavor to administer the required volume (i.e., number of prescribed milligrams) of drug for a period of days. This type of therapy is referred to herein as a dosage-dependent therapy or volume-dependent therapy.
For an infusion device to perform this dosage-dependent therapy accurately, it must maintain a fairly constant infusion rate and determine if any undesired fluctuations in rate occurred. There must be a correction for the amount of drug which was underinfused or overinfused during a period of fluctuation.
For example, if the device were infusing the cytotoxins to the cancer patient too slowly for a period of time, it must determine how many milligrams of drug were not infused and it must then correct for the deficiency by infusing an additional amount of drug for a period of time. After the correction has been made, the pump must endeavor to return to the desired rate so that the prescribed amount of the remaining drug is administered to the patient in the required time period.
The small volumetric errors caused by the mechanism of conventional infusion pumps, as illustrated in the cardiac patient example, are not advantageous in the drug therapy of a cancer patient because they can build up to substantial cumulative errors over a long period of time. This is especially true when the pump is being used in an ambulatory patient who is not subject to continuous surveilance.
It is an object of the method of the present invention to provide physicians with the means for properly administering dosage-dependent therapies.
In recent times it has become increasingly desirable to provide an infusion pump which is compact and lightweight so that it may be used by an ambulatory patient. Ambulatory infusion pumps reduce the need for excess use of hospital facilities and resources. In order to provide a lightweight pump it is highly desirable that a pump require a minimal amount of electric power since power sources, such as batteries, can contribute substantially to the weight of a pump.
It is another object of this invention to provide for a compact, lightweight infusion pump which may be used by ambulatory patients.
There are also an increasing number of applications for which there is a need for a pump which can intravenously administer a plurality of drugs solutions. One such application is the use of chemotherapy to treat such diseases as cancer. Many of the drugs used in chemotherapy and other therapies cannot be mixed together prior to an infusion. Some of these drugs react to neutralize one another. Other drugs react to form precipitates which may block the catheter tube or possibly cause an embolism in the patient.
It is often found that when different incompatible drug solutions are used on a single patient, they are administered by using a separate catheter tube for each drug. A separate infusion pump would then be used on each individual catheter tube line and the tube would deliver the fluid solution into the patient through its respective intravascular access needle. Since a patient must pay for each catheter set and must rent a pump for use with each catheter tube, it becomes costly to use multiple catheter tubes and pumps. There is some danger of infection any time an opening is made in a patient's skin for a catheter. The likelihood of infection increases as more openings are made to accommodate multiple lines.
It is therefore yet another object of this invention to provide a single pump, with a single vascular-entry catheter set, that can deliver a multiplicity of drug solutions without mixing any of them prior to infusion. It is still yet another object of this invention to provide an ambulatory infusion pump which can administer several different drug solutions without mixing any of the fluids together.